The objective of this study is to determine the structure-activity requirements for induction of hepatic mixed-function oxidases by polychlorinated biphenyls (PCBs) and other related halogenated aromatics, and to identify the biochemical changes which occur when rats are exposed to those compounds. Present work includes purification and identification of subspecies of cytochrome P-450 induced by PCBs, phenobarbital, 3-methylcholanthrene and other halogenated aromatics such as chlorinated benzenes. Present work has identified the induction of at least 2 subspecies of cytochrome P-450 by 3,4,5,3',4'5'-hexachlorobiphenyl (HCB) with molecular weights (mws) of 55,000 and 52,000 and an additional 52,000 mw subspecies by 2,3,5,2',3',5'-HCB. These 3 subspecies differed spectrally and catalytically. The present objectives of this work are to: 1) identify the subspecies of cytochrome P-450 induced by these compounds utilizing purification, SDS-polyacrylamide gel electrophoresis, reconstitution, and antibodies to the purified forms.